Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W72/00—Local resource management
  • H04W72/50—Allocation or scheduling criteria for wireless resources
  • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
  • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0045—Arrangements at the receiver end
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1809—Selective-repeat protocols

Definitions

• the present invention relates to a radio communication system and further relates to primary and secondary stations for use in such a system and to a method of operating such a system. While the present specification describes a system with particular reference to the Universal Mobile Telecommunication System (UMTS), it is to be understood that such techniques are equally applicable to use in other mobile radio systems.
• UMTS Universal Mobile Telecommunication System
• HSDPA High-Speed Downlink Packet Access
• Such parameters may include the transmission power, Modulation and Coding Scheme (MCS), spreading factor and number of channelisation codes (in a spread-spectrum system such as UMTS), and delay between retransmissions of a particular packet (or the transmission priority assigned for retransmissions).
• MCS Modulation and Coding Scheme
• UMTS UMTS
• a MS In known radio communication systems, at any one time a MS generally communicates with a single Base Station. During the course of a call the MS may wish to investigate transferring to another BS, for example when the quality of the communication link deteriorates as the MS moves away from its BS, or when the relative traffic loading of different cells requires adjusting.
• the process of transferring from one BS to another is known as handover.
• the MS maintains a list of BSs known as the "active set" with which it is expected that radio links of reasonable quality can be maintained.
• the MS When the MS is in dedicated channel mode, and there are multiple BSs in the active set, the MS is in "soft handover" with the BSs in the active set.
• uplink transmissions are received by all BSs in the active set, and all BSs in the active set transmit substantially the same downlink information to the MS (typically the data and most of the control information would be the same, but power control commands could be different).
• a drawback of this "soft handover" approach is that the uplink and downlink transmission powers cannot be optimised for each individual radio link, as only one set of power control commands is transmitted in the uplink, while the power control commands transmitted over the downlink from different BSs may result in conflicting requirements for the uplink transmission power.
• the normal soft handover procedure is particularly suitable for real time services such as voice links, where a continuous connection must be maintained.
• a problem with the process of fast site selection, as outlined above, is that it may interact badly with the design of an ARQ (Automatic Repeat reQuest) process.
• An example of such an interaction arises if the selected BS is changed before a data packet has been correctly received.
• a further problem with a packet data system is the need for signalling a plurality of separate sets of parameters relating to packet transmission. Disclosure of invention
• An object of the present invention is therefore to provide an improved signalling mechanism.
• a radio communication system having a communication channel between a secondary station and a primary station, the secondary station having receiving means for receiving data from the primary station, acknowledgement means for transmitting a signal to the primary station to indicate whether or not the data was received correctly and parameter signalling means for determining a quality parameter relating to packet transmission and for signalling details of the quality parameter to the primary station, thereby enabling selection of a transmission parameter for subsequent data transmissions, wherein combined signalling is performed by the acknowledgement means and the parameter signalling means transmitting a single code word selected from a plurality of available code words and wherein the primary station has means for receiving the single code word and using the code word in determining whether or not the data was received correctly and the value of the quality parameter.
• acknowledgement and quality parameter signals By combining acknowledgement and quality parameter signals in a single code word, improved operational efficiency is enabled since a reduced set of signals may be used.
• the single code word may be transmitted as a plurality of parts, for example divided between a plurality of time slots in a frame.
• the available code words will comprise a plurality of quality parameter signals and may further comprise, for example, an acknowledgement signal, or a negative acknowledgement signal, or a negative acknowledgement signal and an abort signal.
• an abort signal could indicate that the transmission attempt for that packet should be terminated.
• the secondary station has communication links with a plurality of primary stations and the quality parameter is a site selection signal for indicating a preferred subset of the primary stations for subsequent data transmissions.
• the quality parameter is a channel quality metric, enabling the primary station to determine one or more of the modulation and coding schemes and/or power level to be used for transmission of the next packet. This embodiment may optionally be combined with the site selection embodiment.
• a primary station for use in a radio communication system having a communication channel between a secondary station and the primary station, wherein means are provided for transmitting data to the secondary station, for receiving from the secondary station a single code word, selected from a plurality of available code words, for using the code word in determining whether or not the data was received correctly and the value of a quality parameter, and for determining the value of a transmission parameter for subsequent data transmissions depending on the value of the quality parameter.
• a secondary station for use in a radio communication system having a communication channel between the secondary station and a primary station, wherein receiving means are provided for receiving data from the primary station, acknowledgement means are provided for transmitting a signal to the primary station to indicate whether or not the data was received correctly and parameter signalling means are provided for determining a quality parameter relating to packet transmission and for signalling details of the quality parameter to the primary station, thereby enabling selection of a transmission parameter for subsequent data transmissions, wherein combined signalling is performed by the acknowledgement means and the parameter signalling means transmitting a single code word selected from a plurality of available code words.
• a method of operating a radio communication system having a communication channel between a secondary station and a primary station comprising the secondary station receiving data from the primary station, transmitting an acknowledgement signal to the primary station to indicate whether or not the data was received correctly, determining a quality parameter relating to packet transmission and signalling details of the quality parameter to the primary station, thereby enabling selection of a transmission parameter for subsequent data transmissions, wherein combined acknowledgement and quality parameter signalling is performed by transmitting a single code word selected from a plurality of available code words and wherein the primary station receives the single code word and uses the code word in determining whether or not the data was received correctly and the value of the quality parameter.
• Figure 1 is a block schematic diagram of a radio communication system
• Figure 2 is a block schematic diagram of a radio communication system with a MS in the process of soft handover;
• Figure 3 is a diagram of known UMTS site selection and acknowledgement fields
• Figure 4 is a diagram of a first embodiment of a combined site selection and acknowledgement field
• Figure 5 is a diagram of a second embodiment of a combined site selection and acknowledgement field
• Figure 6 is a diagram of a third embodiment of a combined site selection and acknowledgement field
• Figure 7 is a diagram of an embodiment of a frame and slot structure
• FIG. 8 is a diagram of a combined site selection, link quality and acknowledgement field.
• the same reference numerals have been used to indicate corresponding features.
• a radio communication system comprises a primary station (BS) 100 and a plurality of secondary stations (MS) 110.
• the BS 100 comprises a microcontroller ( ⁇ C) 102, transceiver means (Tx/Rx) 104 connected to antenna means 106, power control means (PC) 107 for altering the transmitted power level, and connection means 108 for connection to the PSTN or other suitable network.
• Each MS 110 comprises a microcontroller ( ⁇ C) 112, transceiver means (Tx/Rx) 114 connected to antenna means 116, and power control means (PC) 118 for altering the transmitted power level.
• Communication from BS 100 to MS 110 takes place on a downlink channel 122, while communication from MS 110 to BS 100 takes place on an uplink channel 124.
• a MS 110 engaged in a soft handover process is illustrated in Figure 2, the MS 110 having three two-way communication channels 226a, 226b, 226c, each comprising an uplink and a downlink channel, with three respective BSs 100a, 100b, 100c.
• the MS 110 receives substantially the same data from each of BSs 100a, 100b, 100c on the downlink channels, and transmits the same data to each of the BSs on the uplink channels.
• each MS 110 receives power control commands determined individually by each of the BSs 100a, 100b, 100c in the active set, but only transmits one set of uplink power control commands to all BSs.
• a MS 110 operates parallel power control loops with each of the BSs 100a, 100b, 100c.
• This modification is particularly useful for HSDPA, in which each data packet is transmitted to the MS 110 from one of the BSs 100a, 100b, 100c, because it enables selection of the best BS on a per-packet basis.
• a proposed embodiment of a HSDPA system for UMTS employs a modified frame structure (with a duration which is a small sub-multiple of a standard 10ms UMTS frame).
• the packet duration is the same as the frame duration.
• Figure 3 illustrates possible data values for each of two data fields included in the frame, a site selection field 302 (site selection being the quality parameter in this embodiment) and an acknowledgement field 304.
• the contents of the site selection field 302 can take one of N possible values, indicating to the infrastructure which BS 100a, 100b, 100c should be used for transmission of the next packet.
• the selection of a BS would be based on measurements of a downlink common pilot channel.
• the indication by the MS 110 of a preferred BS 100a, 100b, 100c may not actually result in that BS becoming selected since the network may take other factors into consideration. Such factors could include load balancing between BSs 100a, 100b, 100c and optimisation of overall system throughput.
• the contents of the acknowledgement field 304 can take one of two possible values, ACK and NACK, where ACK indicates that the most recent packet was received correctly, and NACK indicates that it was not received correctly.
• a further problem is that if the two fields 302,304 are transmitted with the same power level, the relative error rates for the two messages will depend on the number of BSs in the active set. This could be corrected by using different powers for the two data fields, but this may be difficult to arrange and is not currently allowed by the UMTS specifications.
• FIG. 4 illustrates a first embodiment of a combined field 402 with a a possible set of data values.
• transmission of anything other than a NACK in the combined field 403 implies that the last packet was received correctly. If the active set consisted of N BSs, then N+1 different code words would be needed.
• a coding scheme similar to that used for TFCI (Transport Format Combination Indicator) in UMTS could be used, in which each possible data value is mapped to a defined 30 bit code word.
• This scheme also works if there is only one BS in the active set, since it is then equivalent to the conventional ACK/NACK.
• a further advantage of such a scheme is that because one code word is used, there is no need to balance the relative error rates between ACK/NACK and site selection messages. As it is not necessary to send an ACK or NACK unless a packet has actually been transmitted, it may also be desirable to define an additional code word to indicate that there is no information to be signalled in the combined data field 402. In systems without the need for constant envelope transmissions, the need for an additional code word could be avoided by transmitting nothing when there is no information to be signalled.
• Figure 5 illustrates a second embodiment of a combined field 502, in which the transmission of any site selection indication functions as an implicit NACK.
• a normal NACK could be implied by sending a site selection message for the current BS 100.
• the site selection message for any other BS would be treated as ABORT, terminating the ARQ process.
• ABORT terminating the ARQ process.
• An advantage of this embodiment is that the ARQ procedure can be aborted more rapidly than in other proposed schemes, for example those placing a limit on the maximum allowed number of re-transmissions.
• Such a scheme could even be used in the known site selection and acknowledgement scheme of Figure 3, by specifying that sending a NACK at the same time as selection of a different site to that currently transmitting constitutes an ABORT. This would overcome some of the disadvantages of the known scheme.
• ABORT message may depend on the particular embodiment. For example, as described above, it may indicate that the transmission of the current packet should be abandoned. It could also indicate that the further transmission of packets should be abandoned. Typically, an ABORT would additionally imply that reception of the current packet was unsuccessful. There may be more than one criterion for sending an ABORT. For example, it could be sent because the MS 110 has determined that the channel quality has deteriorated too much, or, in the case of delay sensitive applications, some time-out period has been exceeded.
• FIG. 6 illustrates a third embodiment of a combined field 602, in which this problem is solved by adding an ABORT message to the original set of possible signals.
• Figure 7 illustrates one possible uplink frame structure for the control channel.
• a frame 702 has a duration of 2ms and comprises three slots, So, Si and S 2 , of equal duration.
• Each slot comprises four data fields: a pilot field (P) 704, comprising known symbols for channel estimation; a power control field (TPC) 706, comprising power control commands; a combined acknowledgement and site selection field (N/SS) 708; and a Transport Format Combination Indicator (TFCI) field 710.
• P pilot field
• TPC power control field
• N/SS combined acknowledgement and site selection field
• TFCI Transport Format Combination Indicator
• One power control command could be sent in every slot.
• the N/SS information from the three slots So,S ⁇ ,S 2 in the frame 702 is combined to form one code word.
• the TFCI information (if present) would be combined over 5 frames (i.e. 10ms), to indicate the format of any data sent in the uplink.
• the method of sending uplink data may be
• the MS 110 may have a communication link with a single BS 100 (in which case no site selection information is required) or, as in the above embodiments, with a plurality of BSs 100 (in which case site selection information may be required).
• the link quality information enables the BS 100 to determine which Modulation/Coding Scheme (MCS) and/or power level should be used for transmission of the next packet.
• MCS Modulation/Coding Scheme
• Methods of deriving appropriate link quality information are well known.
• the quality information could be based on measurements of SIR (Signal to Interference Ratio) on a downlink common pilot channel or a dedicated channel.
• acknowledgement and link quality information are signalled separately, in a similar manner to that described for site selection information in relation to Figure 3 with the site selection field 302 replaced by a link quality field which can take one of N possible values.
• the operation and implementation of the system is much simpler if the MCS not updated when a failed packet is re-transmitted.
• the acknowledgement field in 304 response to transmission of a particular packet is a ACK
• the link quality information is used to determine the MCS for the next packet.
• the packet is not received correctly and a NACK is transmitted, the packet is retransmitted using the same MCS as the original transmission.
• This proposed scheme suffers from a similar problem to the site selection scheme discussed above, in that it is inefficient to send both ACK/NACK and quality in separate data fields, since not all combinations may be needed. Essentially, if change of MCS during an ARQ cycle is prohibited, then quality information need not be sent at the same time as a NACK.
• a further problem similar to that of the site selection embodiments above, is that if the acknowledgement and quality fields are transmitted with the same power level, the relative error rates for the two messages will depend on the number of possible quality levels to be signalled. This could be corrected by using different powers for the two data fields, but this is not currently allowed by the UMTS specifications.
• a single data field is used to convey both acknowledgement and link quality information.
• a first embodiment of a combined field is based on that illustrated in Figure 4, with data values indicating site selection in Figure 4 replaced by data values indicating particular link quality information.
• transmission of anything other than a NACK in the combined data field indicates that the last data packet was received correctly. If N different quality levels can be signalled, then N+1 different code words would be needed.
• Other aspects of the embodiment are identical to those discussed above.
• a second embodiment of a combined field is based on that illustrated in Figure 6, in which an ABORT message is added to the original set of possible signals to terminate the ARQ sequence early.
• FIG. 8 illustrates an example of a embodiment of a combined site selection and link quality field 802, in which N sites (S1 to SN) and M link quality values (Q1 to QM) can be signalled. As with the embodiment shown in Figure 4, transmission of anything other than a NACK in the combined field 802 indicates that the last packet was received correctly.
• the number of valid code words and the meaning of each possible code word may be defined when the radio channel is set up or reconfigured.
• the meaning of each word may be context dependent, for example the number of possible quality parameter values may vary with the number of BSs 100 in the active set. Further, signalling of some quality parameters may convey an implicit acknowledgement while signalling of others may convey an implicit NACK.
• the contents and size of the set of possible quality parameters may depend on whether the packet was received correctly. For example, if a packet is received incorrectly the range of quality values which need to be signalled may correspond to lower quality values than if the packet is received correctly. The number of quality values which can be signalled may also be different in these two cases.
• the setting of transmission parameter values may be the responsibility of a variety of parts of the fixed infrastructure, for example in a "Node B", which is the part of the fixed infrastructure directly interfacing with a MS 110, or at a higher level in the Radio Network Controller (RNC).
• RNC Radio Network Controller
• base station or “primary station” is therefore to be understood to include the parts of the network fixed infrastructure responsible for the determining and setting of transmission parameter values.
• the present invention is not restricted to use in such a system and may be applied in a wide range of systems, for example including
• TDD Time Division Duplex
• the data channel is transmitted to the MS 110 from one BS at a time.
• the set of available site selection words could also include words which indicated the selection of a plurality of BSs.
• the invention could be applied to radio links at different frequencies which therefore require separate power control even if they are between the same pair of stations.

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